The organic electroluminescence element (hereinafter, “electroluminescence” may be occasionally abbreviated as “EL”) generally has a multilayer structure wherein plural layers are laminated using materials having a hole or electron injecting, transporting and blocking functions in order to achieve long-lasting life and high efficiency. Further, the organic EL element having the multilayer structure generally has a blocking layer, which prevents penetration of holes and electrons to the counter electrode, provided between an electrode and a light emitting layer to efficiently block holes and electrons in the light emitting layer.
However, there is a concern with the organic EL elements having the multilayer structure that deterioration caused during its driving at interfaces of the respective layers will lower the luminous efficiency or will deteriorate the elements to lower its luminance. In particular, charges are easily builtup at interfaces with the organic EL element comprising a blocking layer so that deterioration is easily caused at interfaces and the luminance deterioration of the element is a concern.
In order to restrain the deterioration from causing at interfaces of the respective layers during driving, methods to arrange materials used for the hole injecting and transporting layer and the electron injecting and transporting layer are proposed.
For example, the Patent Document 1 discloses a method to improve the injection properties of holes from an anode and the injection properties of electrons from the cathode, wherein an organic semiconductor layer (hole injecting and transporting layer or electron injecting and transporting layer) is constituted from either of the followings: an organic compound and an oxidizing dopant, an organic compound and a reducing dopant, or an organic compound and a conducting fine particle.
However, the organic EL element of the Patent Document 1 has the above-mentioned concerns of lowering in the luminous efficiency of causing and the deterioration of elements because an inorganic charge blocking layer (blocking layer) is provided between the organic semiconductor layer (hole injecting and transporting layer or electron injecting and transporting layer) and the organic light emitting layer.
Further for example, the Patent Document 2 discloses a method of doping an electron accepting dopant to an organic compound layer contacting to an anode, and an object thereof is to lower the energy barrier caused in injecting holes from the anode to the organic compound layer (hole injecting and transporting layer). Moreover, for example, the Patent Documents 3 and 4 discloses a method of doping an electron donating dopant to an organic compound layer contacting to a cathode, and their respective object is to lower the energy barrier caused in injecting electrons from the cathode to the organic compound layer (electron injecting and transporting layer).
Patent Document 1: Japanese Patent Application Laid-Open (JP-A) No. 2000-315581
Patent Document 2: JP-A No. 11-251067
Patent Document 3: JP-A No. 10-270171
Patent Document 4: JP-A No. 10-270172